1. Field of the Invention
The present invention relates to a network communication system utilizing wireless communication. The invention more particularly relates to a wireless computer network in which plural groups can perform network communication through different channels at the same time. For example, the above network communication system can be applied to an indoor or mobile wireless communication system.
2. Description of the Related Art
As to known publications describing conventional network communication systems, there exists, for example, Japanese Laid-open Patent Publication No. 6-29981/1994. This publication discloses a local area network (LAN) for receiving signals on a wireless transmission channel. The local area network includes a receiver and a transmitter. In order to realize a LAN with high efficiency, the LAN also includes a received signal level determining apparatus, a threshold level circuit apparatus for generating a level indication signal, and a controller for controlling the operation of the transmitter in accordance with the level indication signal.
Japanese Laid-open Patent Publication No. 5-260051/1993 proposes a wireless system capable of causing the base station to take a role of repeater and smoothly performing the operations of transmitting and receiving signals between the respective terminals by dividing the usable frequency zone into three areas including a message channel, a channel tone Up, and a channel tone Down. The network includes plural wireless terminals and a base station capable of performing the operation of transmitting and receiving the signal between the base station and all of the wireless terminals. This wireless system does not need communication cables connecting each of the terminals.
The wireless LAN described in the specification of Japanese Laid-open Patent Publication No. 6-29961/1994 utilizes the access system (CSMA) in the same manner as used in the popular Ethernet system; that is the wireless LAN of the symmetrical type jointly occupying the same wireless channel at all of the respective terminals. Furthermore, the wireless LAN described in the specification of Japanese Laid-open Patent Publication No. 5-260051/1993 is the wireless LAN with a base station which controls the wireless channel in order to improve the communication throughput.
In recent years, the number of notebook type portable personal computers (PCs) has increased. Furthermore, assuming that the palm-top computer, often called a portable information terminal or data assistant, starts to be used, users of these portable computers will go out from different or the same places and meet together carrying their portable computers and utilize the wireless network regardless of the place where they ordinarily work. In this situation, an environment in which communication can be performed properly is needed. The above-described network including portable computers is referred to as a mobile network.
It seems that there exist many environments in which the above mobile network is adjacently employed for each group of plural users. Further, on many occasions, the frequency of transmitting and receiving the required data in real time such as meeting increases, and thereby the traffic is raised. Consequently, in the wireless LAN as described in the specification of the above Japanese Laid-open Patent Publication No. 5-29961/1994 in which only one wireless channel is used (jointly occupied) by all of the respective terminals, there arises apparently a problem of causing a decrease in throughput.
Furthermore, in the wireless LAN as described in the specification of the above Japanese Laid-open Patent Publication No. 5-260051/1993, since it is necessary to provide a repeater such as the base station, the restriction of the place that the network can be constructed only at the place where the base station is installed arises inevitably.
Accordingly, it is an object of the present invention to solve the above-mentioned problems.
It is another object of the present invention to provide a wireless network communication system and method for selecting the wireless channel (the PN or spread code) when a group intends to start the communication or during the period of communication in order for different groups of terminals to perform communication at the same time.
The present invention solves the above-described problems by properly selecting the pseudonoise PN code to be used. The PN code can be determined by analyzing each possible PN (spread) code which can be used and determining if the code is vacant. Subsequently, a confirmation packet is transmitted. If another group is using this PN code, the other group will transmit a busy packet indicating that the PN code is not available. Subsequently, the next PN code which was earlier determined to be vacant will be checked.
Alternatively, it is possible to initially determine whether the PN codes are vacant by sensing each of the possible PN codes in different orders by different groups of terminals which can be simultaneously operating. This will reduce the chances of two different groups simultaneously determining that a PN code is available.
As a further alternative, it is possible to randomly check if the PN codes which have been sensed as being vacant are actually vacant. This is done by randomly selecting the vacant codes and transmitting a confirmation packet and waiting for the receipt of a busy packet. If a busy packet is not received, the PN code is determined to be available.
As an alternative to the above-described embodiments, it is possible to sense whether individual PN codes are available and then once a single PN code is determined to be vacant, sending out the corresponding confirmation packet and waiting for the receipt of a busy packet. In contrast, the other embodiments determine each of the vacant codes by analyzing all codes at once. It is also possible for the codes to be sensed such that each group which is to begin communication senses the free channels in different orders. It is also possible to sense the different channels in random orders.
As a further embodiment, all of the vacant PN codes may be determined. As described above, confirmation packets may be sent out and if the PN code is being used, a busy packet may be received. However, instead of simply indicating that the desired PN code is busy, the PN code may include information which describes a code which is vacant and may be used or further checked.
Each of the above-described embodiments has a host terminal of a group perform the checking of the availability of the PN code. Also, it is the host terminal of the other groups which transmit the busy packet. However, it is possible that one of the terminals in the other group may be within communication range of the group desiring to be set-up but the host terminal of that other group is out of communication range of the group desired to be set-up. Accordingly, it is possible to have each of the terminals of the groups which are already communicating monitor for the transmission of the confirmation packet and transmit a busy packet which is received. Thus, if a host terminal of another group is out of range, one or more other terminals within that other group can transmit the busy packet.
As a further alternative, instead of transmitting a confirmation packet, it is possible for the other groups to periodically transmit a busy packet. Thus, there is no need for the group desiring to have its communication set up transmit a confirmation packet as the busy packet will be transmitted by the other groups every predetermined period of time.
As further embodiments, the host terminal of a group desiring to set up communication can attempt to communicate on one of the PN channels. If information is received in response to this communication, the channel is being used by another group and cannot be used. As an alternative, the throughput of the channel being checked can be determined or it can be determined if there is the carrier sensing frequency is greater than a threshold value in order to determine a vacant PN channel. The PN codes may be checked in different orders by different groups desiring to begin communication or alternatively, the different groups desiring to being communication may randomly select the groups to communicate. As a further alternative, the host terminal desiring to start communication for a group may transmit an inquiry packet and receive an information packet in order to determine the code for communication. Further, a correlation value may be sensed for the vacant channels and the inquiry packet can be sent using the PN code which corresponds to the maximum correlation value.
It is another object of the present invention to provide a communication system and method in which a plurality of groups perform network communication at the same time by the use of different wireless channels by preparing plural wireless channels with very small interference and by selecting one wireless channel at the time of constructing the network based on other channels used by other groups.
These and other objects are accomplished by a novel wireless communication network in which groups optionally constructed (ad-hoc) with the plural wireless terminals perform symmetrical type network communication between the respective wireless terminals belonging to a same group. The network communication system is constructed such that when a group performs network communication, any one of the wireless terminals belonging to the group detects the communication channel being employed in one or more other groups, determines the vacant (unused) communication channels, and selects the vacant communication channel to be employed by the above group. Thereafter, the communication channel thus selected is notified at least to the other wireless terminals belonging to the group. After the other wireless terminals confirm the communication channel to be employed by the group members, the symmetrical type network communication is started and uses the above communication channel.
In an embodiment, the communication channel selected for the group is code-divisionally multiplied by the PN (pseudonoise) code individually selected (employed) for the groups. Communication in the same group detects the presence or absence of the spread-spectrum signal of the aforementioned individual PN code, and when the spread-spectrum signal is not detected, the transmitting operation is done.
Therefore, it is possible to provide a wireless system which uses a carrier of a single frequency as the carrier to be employed for transmission, and plural wireless communication groups can coexist with small interference.
As another alternative, the communication channel employed in the groups may be frequency-divisionally multiplied by the frequency individually selected for the respective groups. The communication performed by a group detects the presence or absence of the signal in the aforementioned individual frequency, and when the signal is not detected, the transmitting operation is done.
Consequently, it is possible to provide a wireless system in which by allocating the carriers of plural different frequencies to the respective wireless channels, plural wireless communication groups can coexist with very small interference.
With the present invention, it is possible to provide a wireless system in which the plural groups can perform network communication at the same time using different wireless channels, and in the wireless system thus realized, lowering of the throughput can be suppressed. Furthermore, the network environment can be freely constructed regardless of the place where the network is installed.